1. Field of the Invention
This invention relates to radioactivity well logging and, more particularly, to a method utilizing natural ray gamma ray logging to determine the optimum locations along the length of a borehole penetrating earth formations to initiate well stimulation operations or, if the borehole is cased, the optimum location for perforation operations.
2. Description of the Prior Art
Various models and apparatus have been utilized in the well logging art to study the radioactive properties of subsurface formations, both where the radioactivity is natural and where it is artificially induced. In general, such methods and apparatus when applied to the field of natural gamma ray well logging having utilized three channels of spectra centered on the 1.46 MeV potassium-40, the 1.76 MeV uranium, and the 2.62 MeV thorium energies. Further, such prior art techniques have been directed to utilizing the logs to locate so-called "source rocks" for oil production in regions being explored.
One such technique utilizes natural gamma ray logs to determine the characteristics of shale formations as described in U.S. Pat. No. 4,017,755, issued Jan, 31, 1938 to Supernaw et al. Supernaw et al is directed to determining the amount of organic carbon contained within the shale formation and utilizes the gamma ray logs to derive potassium/uranium or thorium/uranium which, when compared with the organic carbon at selected depth points within the borehole are used in deriving curves indicative of the organic carbon contained within the shale deposit. As in most prior art techniques utilizing the natural gamma ray logging technique, Supernaw et al is specifically directed to locating hydrocarbon bearing strata but not to determining optimum locations for performing well stimulation operations or casing perforating operations within the boerhole adjacent to the located hydrocarbon bearing formations to improve recovery of the subsurface hydrocarbons.
Accordingly, the present invention overcomes the deficiencies of the prior art by providing a method for utilizing information derived from the natural gamma ray well logging of the borehole to provide information relating to the optimum locations within the borehole to conduct well stimulation operations or, where the borehole is cased, to conduct casing perforation operations.